1. Field of the Invention
The present invention relates to thermal sensing, and more specifically to methods and apparatus for a programmable thermal sensor in an integrated circuit.
2. Art Background
Advances in silicon process technology has lead to the development of increasingly larger die sizes for integrated circuits. The large dies sizes permit integration of millions of transistors on a single die. As die sizes for integrated circuits become larger, the integrated circuits consume more power. In addition, advances in microprocessor computing require execution of a large number of instructions per second. To execute more instructions per second, the microprocessor circuits operate at an increased dock frequency. Therefore, a microprocessor containing over one million transistors may consume over 30 watts of power. With large amounts of power being dissipated, cooling becomes a problem.
Typically, integrated circuits and printed circuit boards are cooled by either active or passive cooling devices. A passive cooling device, such as a heat sink mounted onto an integrated circuit, has a limited capacity to dissipate heat. An active cooling device, such as a fan, is used to dissipate larger amounts of heat. Although a fan cooling system dissipates heat, there are several disadvantages associated with such a system. Traditionally, fans cool integrated circuits by air convection circulated by a fan. However, when a fan is used in conjunction with a high density multi-chip computer system, a large volume of air is required for cooling thereby necessitating powerful blowers and large ducts. The powerful blowers and large ducts implemented in the computer occupy precious space and are too noisy. The removal of a cover or other casing may result in a disturbance of air flow causing the fan cooling system to fail. In addition, the fan cooling system is made up of mechanical parts that have a mean time between failure (MTBF) specification less than a typical integrated circuit. Furthermore, fan cooling systems introduce noise and vibration into the system.
In addition to cooling systems, thermal sensors are implemented to track the temperature of an integrated circuit or electronic system. Typically, thermal sensors consist of a thermal couple which is directly attached to a heat sink. In more sophisticated thermal sensing systems, a diode and external analog circuitry are used. In operation, the voltage/current characteristics of the diode change depending upon temperature of the integrated circuit, and the external analog circuitry measures the voltage or current characteristics of the diode. The additional analog circuitry is complex and difficult to implement. In addition, employing the analog circuitry results in a thermal time delay degrading the accuracy of such a configuration. Moreover, external analog circuitry for sensing the voltage of the diode consumes a larger area than the integrated circuit being sensed. Therefore, it is desirable to provide a thermal sensor which is incorporated into the integrated circuit. In addition, it is desirable to provide a thermal sensor that can provide feedback for an active cooling system. Furthermore, it is desirable to control the temperature of an integrated circuit without the use of a fan. The present invention provides an integrated thermal sensor that detects a threshold temperature so that active cooling of the integrated circuit is accomplished through system control.